cobalt

Are you talking 1st gear? I have the HF turbo with B&B headers and i am seeing boost starting at 2500 - 2700rpms in first with full boost by about 3200 rpm. In second on up I am seeing boost starting at 2000 - 2100rpms with full boost by about 2600rpm.

Vince5

I must admit I have not checked 1st gear. I am more talking 5th gear cruising at 3rpm, with no boost at all then nailing it. It would take her a little while to wake up and I would get full boost just under 4000 rpm.

When on the track I don't really have time to check

straight6

Heard a 964 T with cat and muffler bypass today, AWESOME!! I'm doing it!
Can always go back... Back pressure not an issue. Old wives tale!!

cobalt

Straight6

Get ready to throw flames. Without the cat or the muffler you will be seeing a light show at night out your review mirror. I will be sending you a PM later.

straight6

Hey Anthony,
Looking forward to the fireworks!!

maverick

I am not running any cats and have the B&B headers and Techart muffler. She is not to loud at idle and low speed but step on it and it is reminiscent of the Mulsane straight! Flames at night ....oh yeah!
I have not noticed any loss of power.

straight6

Yippie!!!!!

James.E

I have dyno'd just about every combo of exhaust mod there is, on the same dyno. As I recall the muffler is worth about 5rwhp. The stock muffler is actually very free flowing. It is basically the same as a J pipe with holes in and then boxed in.

Headers are worth 15 rwhp, however they normally have a crap waste gate pipe design that effectively recalibrates your wastegate and hence you'll generate more boost. This often has the effect of boosting rwhp by as much as 40bhp. If you dyno your car do runs in 4th and 5th, you'll be shocked.....

The cat bypass is def. the one to go for. Dosn't sound quite as good as a J-pipe but it is worth at least 15 rwhp.

emilios

James,

do you mean that the cat bypass is not as loud as a J-pipe?

James.E

The overrun pops and bangs are more muffled when you have muffler and no cat. If you keep the cat and have no muffler I think that sounds the best but you'll be down on bhp relative to the other option. The other thing to remember with the cat is that they don't like neat fuel and when you think how rich most of these cars run you'll understand why your cat is almost certainly not working properly or just blocked sapping more power. Removing the cat also increases throtle responce.

C2 Turbo

Can someone please tell me what contributes more to the loudness,a cat bypass or the muffler bypass ? Currently my car has a B&B headers and B&B exhaust system with no cats.Though the car feels very strong & responsive but i really can't afford/don't like the loudness factor especially when i go to the Doctors parking area
So the general censes is to keep the cats ( or get a 100 cell one ) and get the muffler bypass,right ? Than my next question is what make muffler bypass is compatible with the B&B headers & the stock cats. ? O btw what exactly is a CBV and how does it work ?
Flew to Hershey swap meet to check out some tricked out C2 Turbos and was really disppointed to see only 3 of them and guess what,all stock Thanks.

emilios

Well, they are quite rare beasts Yasir..

Staffan

Muffler by-pass is the loud alternative of the two.
Also RUF claims that you loose about 15hp if you replace the stock muffler with a by-pass. Instead you gain that amount by removing the cat, the car gets so much more responsive and will reach full boost sooner.

I have an empty stock cat with a stock muffler, not louder than stock, perhaps a little bit deeper sound. The cat has very little to do with the sound.

The stock muffler is for some reason underestimated, didn't they use the stock muffler but no cat on the IMSA cars, someone on the board must know ?

Do a search on this board about CBV, you will find more information than you need. Short version, if you have a stock CBV (plastic black Bosch part) the recommendation is to replace it, broken or not. It's a part that is known to fail, mine was broken, didn't know that it was.

If you have a broken CBV your boost will drop significantly between shifts and there will be a totaly unecessary pressure on the throttle.

straight6

My tech says that losing HP without the stock muffler is nonsense. He is big on bypassing the whole deal...

cobalt

I don't think there should be a difference either way. The stock muffler is just a big can. the stock muffler has a J bend pipe that goes into the can and has a series of holes in it to vent the gases behind a baffle plate to reduce noise. The J pipe basically mimics the stock muffler without having to go through the baffle therefore allows more sound. Hp should not be altered you may reduce back pressure a wee bit but who cares it sounds much better.

Fabspeed recommends the cat bypass with the stock muffler.